One of the methods known of developing into visible printed impression the latent electrostatic images created on the surface of the recording medium is the magnetic brush method. In this method, which is based on the use of a magnet roller, it is well known that developing performance depends much upon the way the magnet roller transfers the powdery developer.
Yamashita et al. U.S. Pat. No. 3,828,730 discloses a cylindrical permanent magnet structure for use in developing an electrostatic image, in which an odd number of axially extending magnetic poles is utilized. The developing apparatus of that patent is, however, subject to clogging by the developer powder, thereby imposing undesirable load and reducing performance.
An object of the present invention is to provide a magnet roller which readily and with high efficiency releases the adhering particles of powdery developer from the surface of its rotating sleeve after the particles have moved through the region of magnetic brush formation where the developing action takes place. Another object of this invention is to provide a magnet roller which picks up a proper amount of powdery developer from the pool in the containing vessel to transport it to the magnetic brush region so that a magnetic brush suited to developing action will be maintained at all times in operation. Another object is to provide magnetic rollers which mix the toner and carrier components of the picked-up or adhering powdery developer so that a more thoroughly and uniformly mixed powder will be brought into the developing region, which produce developed images high in quality, or which cost much less to manufacture and are adapted to high-performance developing.